The toxic chemical made infamous in Julia Roberts hit Erin Brockovich has been found in extremely high levels in groundwater at a Japanese plant. Source: Supplied

THE toxic chemical made infamous by campaigning single mother Erin Brockovich has been found at up to 15,800 times safety limits in groundwater at a Japan iron plant, the factory's operator said Thursday.

Excessive amounts of hexavalent chromium were discovered at Nippon Denko's plant in Tokushima in the country's west as it prepared to halt production of chromium salts at the sixties-era factory, the firm said.

Also known as chromium-6, cancer-causing hexavalent chromium was at the centre of the 2000 US film Erin Brockovich, which starred Julia Roberts as a real life legal assistant who leads a battle against a California power company accused of polluting a city's water supply.

At the Japanese plant, the chemical was found at up to 400 times safety limits in soil and up to 15,800 times allowable levels in groundwater, Nippon Denko said, but added that "no hazards to human health or the outside environment" were reported.

"We voluntarily surveyed the soil and groundwater at the plant between June and August before the closure," a company spokesman said, adding that two dozen locations on the site were tested.

"At the moment, we're assuming the contamination is limited to the plant's compound and that no adverse effects have been caused to surrounding areas," a local government statement said.

The authority said its own survey had found no traces of the chemical in water surrounding the plant, which sits on landfill, or in wells on the fringes of the facility.

The company said it was planning to enclose contaminated areas with 11 metre containment walls to prevent seepage of the tainted groundwater.

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